Future television receivers are likely to be based on wideband multi-channel receiver technology, known as Full Spectrum Reception (FSR) technology.
In the FSR approach, wide-band digitization is used to capture the complete composite input signal. In the case of cable television signals, the complete TV band between DC and approximately 1 GHz is captured with a high speed Analog-to-Digital Converter (ADC). This approach has many benefits over the traditional analog tuner based approach. For example, a large number of tuners can be realized at minimal hardware cost. The FSR approach also enables new features which cannot be economically realized with the traditional analog approach, such as fast channel changing and faster service scanning of available channels. In order to realize a faster service scan, spectral analysis of the input signal is required.
During initial installation of a conventional receiver, a table is generated with centre frequencies of all available channels. If this information is not broadcast by the network operator, for example by means of a dedicated channel known to the receiver beforehand, the receiver needs to scan the whole spectrum in order to locate channels. Traditional scanning is slow because every frequency has to be tested to determine whether a channel is present. If, however, an accurate measure of the entire spectrum can be more quickly made, the location of each channel could be determined from this, removing the need for a full scan.
Digital television broadcasting—compliant with, for example, DVB, ATSC, or ARIB standards—involves transmitting an MPEG2 Transport Stream at a certain channel (frequency) within a particular medium (terrestrial, satellite, or cable). A particular modulation scheme (e.g. PSK, QAM, OFDM, VSB) is used to modulate the Transport Stream data within the channel of the particular medium. Typically, a plurality of services, for example in the form of television programmes with associated information (e.g. alternate audio streams, subtitles and interactive data content), will be carried by a single transport stream on a single channel.
Digital television receivers will normally be equipped with service presets. By keying in a specific number on a remote control the user can start watching a particular service (e.g. NBC, BBC1, Nederland 1 etc.). When the digital television receiver is first deployed in a new environment, for example when a user buys a new television and installs it at home, it is necessary to perform a service scan in order to obtain information about all the channels that may be available. In a service scan, the entire television band is scanned for the presence of television (and other) services, and information relating to the available services is stored in the memory of the receiver. Each of the individual services will be associated with a certain preset (i.e. a given number). The service scan may also need to be repeated at some later time, for example if the channel allocation of services is changed or new services are added.
Conventional digital television receivers are equipped with one, or possibly more than one, tuner. Such a tuner is capable of tuning to a channel at a certain frequency and subsequently providing the baseband signal in that channel to a demodulator (e.g. DVB-S, DVB-C, or DVB-T). The demodulator will subsequently provide an MPEG2 Transport Stream to the Transport Stream de-multiplexer. The Transport Stream de-multiplexer is able to extract coded audio and video data, but also meta-data about the services present in the Transport Stream (e.g. service-id and service-name as encapsulated in tables such as PAT and PMT).
In the known art a service scan is performed as follows:
 for (f=startfreq; f < endfreq; f += stepsize) { Tune tuner to frequency (f); if (signal_present) /* tuner locks */  {Try to demodulate baseband signal;if (transport_stream_present) /* not all signals may be DTV broadcast */ {  Demultiplex transport_stream and extract meta_data;  Store channel preset based on meta_data; } }}
In digital television applications, for example with MPEG2 transport stream, a single channel may contain multiple TV services, leading to multiple presets. More than one channel preset may in such cases be stored for a single detected signal.
Following the above algorithm, the tuner sequentially scans the entire band, scanning over all frequencies (from startfreq to endfreq) at a given resolution (defined by stepsize). If the tuner locks (signal_present), and the baseband signal contains a properly modulated Transport Stream (transport_stream_present), the meta data is extracted and stored in the memory of the receiver.
The above process can be very time consuming, typically taking tens of minutes or even hours, particularly if the resolution (stepsize) has to be chosen to be small to ensure that all available channels are identified. If the channels are mapped to a fixed frequency grid that is known in advance, the process can proceed more quickly, because the value for stepsize can be chosen to match the present grid pattern. This is typically the case for terrestrial digital television transmissions, but not for satellite transmissions.
Many methods are known to exist for speeding up a service scan. All of these known methods are, however, based on having a priori information available about the service and channel allocations in the band over which a service scan is to be performed.
It is known that a service on the internet can provide all available channel and service allocations for a certain medium. The user only has to enter his locality (e.g. ZIP-code) and optionally a service provider from a short list. The internet service can then provide all the necessary data, which can be stored immediately into the receiver memory without the need for a conventional service scan. An example of such a system is in Windows Media Center in Microsoft Windows Vista. A similar kind of system is disclosed in international published patent application WO 2005/015738. Internet connectivity is not, however, always necessarily available and may not be present when installing a receiving unit, particularly a stand-alone digital television receiver.
Another known solution for a faster service scan involves a service provider providing a full database of channel and service allocations as an integral part of the broadcast service. At least one channel will have a so-called Network Information Table (NIT) included in the Transport Stream. This NIT contains all necessary information, which can be stored directly into the receiver memory. The receiver only requires to be supplied with the frequency of the channel containing the NIT in order to receive all available channel information. In a vertical service offering (i.e. where one provider maintains control of all channel information as well as the receiver factory configuration), the receiver (STB) may come pre-configured with this one particular frequency. This solution would work well if a single provider owns the medium. This is typically the case for cable providers, but if multiple providers or broadcasters share a single medium (e.g. terrestrial broadcast or satellite transponders) this is less likely to be the case.
In summary, currently known fast scanning solutions tend to be based on having a priori information about available channels being present. This information may be provided either out-of-band (e.g. via the internet) or in-band (e.g. via a NIT on a dedicated channel). When such information is not available (for example in the cases of there being no internet connection or more than one service provider), these solutions do not work and a lengthy ‘brute force’ service scan is necessary. This is a particular problem a fixed frequency grid is not defined, which is the case for satellite television.
Although a lengthy service scan operation may be a one-off operation, further service scans may need to be carried out when the channel list is updated. It would therefore be advantageous to speed up the process of performing a full scan for available channels.